Not being an aficionado of the Marvel Comics hero Thor, not to mention Norse mythology, I approached this new lollapalooza with an open mind that was quickly addled by loads of back story and front story and an ear-splitting avalanche of special effects – in IMAX 3-D no less, just in case bodies and hammers hurtling straight at you in 2-D seems hopelessly passé.

"Thor" begins in the New Mexico desert – ground zero for all things extraterrestrially spooky. Astrophysicist Jane Foster (Portman), her mentor Dr. Erik Sevig (Stellan Skarsgård), and sidekick Darcy (Kat Dennings) are investigating an atmospheric disturbance when a big, bearded stranger – that would be Thor, played by hunky Australian soap star Chris Hemsworth – knocks into their RV.

From here, the film, which was written by Ashley Miller, Zack Stentz, and Don Payne, flashes back and forth between Earth and the floating kingdom of Asgard, where Thor's white-bearded father, Odin (Hopkins), has had his hands full. In the run-up to Odin's coronation of Thor as his successor, the Frost Giants of Jotunheim, perpetual foes who seem to have cornered the market on pointy chins, crash the party. This sends Thor into a tantrum of retribution so unseemly that Odin ends up stripping him of his powers and banishing him to Earth, leaving his slit-eyed half-brother Loki (Tom Hiddleston) to ply his own hubris.

Branagh seems to have confused the sequences involving Odin and Thor with Shakespeare at his most doomy. In most other respects, this $150 million epic is monumentally cheesy. The special effects in the Asgard scenes are scaled big, and the Earth scenes, by deliberate contrast, are rather plain. As a result, I felt continually wrenched not only between two worlds but also between two very different kinds of headaches.

In a film like this, talented actors are often caught in a bind. Do I try to give a real performance – Hopkins's rather poignant solution here – or, à la Hemsworth and Portman, do I wink at the audience? I prefer the goofier approach, which is why, even though Hemsworth isn't going to be cast in "King Lear" anytime soon, he's the best thing about "Thor." He's absorbed the central lesson of his musclehead movie forebears: Beefcake is best when it's making fun of itself. Grade: C+ (Rated PG-13 for sequences of intense sci-fi action and violence.)